Air-fuel ratio control system for automotive engines

ABSTRACT

An air-fuel ratio control system for an engine has a feedback control system operated in accordance with an output voltage of an O 2  -sensor. When the output voltage becomes higher than a reference voltage, the operation of the feedback control system starts. The reference voltage is set to a high level when the engine is started, and set to a low level when a set time elapses after the starting of the engine.

BACKGROUND OF THE INVENTION

The present invention relates to a system for controlling air-fuel ratioof mixture for an automotive engine, and more particularly to a systemfor detecting an activated state of an O₂ -sensor for restarting theengine.

The O₂ -sensor does not produce a normal output voltage before thetemperature of the sensor body rises above an activation temperature.Accordingly, an air-fuel ratio control operation using a feedback signalfrom the O₂ -sensor must be started after the activation of the O₂-sensor.

The activation of the O₂ -sensor can be determined by the fact that theoutput voltage of the O₂ -sensor exceeds a predetermined referencevalue. For example, Japanese Patent Application Laid Open No. 58-8246discloses a control system in which the sum of the output voltage of theO₂ -sensor and a standard voltage is compared with a reference voltage.

However, there is a problem in the detection by the output voltage ofthe O₂ -sensor. Namely, if the engine is re-started in the conditionwhen the temperature of the O₂ -sensor is in a low temperature range,the O₂ -sensor produces a high error voltage for a period of time inspite of an inactivated state. In order to avoid such a malfunction, ifthe reference voltage is set to a high value, a long time elapses beforestaring the feedback operation in normal warming up of the engine.

SUMMARY OF THE INVENTION

Accordingly, the object of the present invention is to provide a controlsystem which may prevent erroneous feedback control operation in anair-fuel ratio control system.

The air-fuel ratio control system for an automotive engine has an O₂-sensor producing an output voltage relative to oxygen concentration ofexhaust gases of the engine, and a feedback control system responsive tothe output voltage of the O₂ -sensor for controlling the air-fuel ratioof the mixture supplied to the engine.

In accordance with the present invention, the system comprises detectingmeans for detecting starting of the engine and for producing an enginestart signal, a timer responsive to the engine start signal forproducing a first timer signal during a predetermined period of time andfor producing a second timer signal after the predetermined period oftime, O₂ -sensor warm-up detecting means responsive to the first timersignal for comparing the output voltage of the O₂ -sensor with a highlevel reference voltage and for producing a feedback control startsignal when the output voltage of the O₂ -sensor exceeds the high levelreference voltage, and responsive to the second timer signal forcomparing the output voltage of the O₂ -sensor with a low levelreference voltage which is lower than the high level reference voltageand for producing the feedback control start signal when the outputvoltage of the O₂ -sensor exceeds the low level reference voltage. Inresponse to the feedback control start signal, the operation of thefeedback control system starts.

Since the reference voltage for detecting the activation of the O₂-sensor is set to a high value for the predetermined time after startingthe engine, the detection of the activation can be done withoutmalfunction, and the feedback control operation by the feedback signalof the O₂ -sensor is started at a proper time. Further, since thereference voltage is changed to a low level when the predetermined timeelapses, the feedback control operation starts at a proper time at coldengine operation without delay.

The other objects and features of this invention will become understoodfrom the following description with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic block diagram showing a system of the presentinvention; and

FIG. 2 is a flowchart showing the operation of the system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, an automotive engine 1 has an intake pipe 4, athrottle body 5 and an intake manifold 6. Air is induced in the enginepassing through an air cleaner 2, air flow meter 3 and throttle valve 9.An O₂ -sensor 12 is provided on an exhaust pipe 7 at a position upstreamof a catalytic converter 8. A fuel injector 10 is mounted on thethrottle body 5 and a coolant temperature sensor 13 is mounted on awater jacket which is provided for pre-heating the intake air passingthrough the intake manifold 6. An engine speed sensor 11 is provided forproducing an engine speed signal, and an ignition coil 14 is providedfor producing an engine starting signal at the start of the engine.

Output signals of the air flow meter 3, sensors 11, 12, 13 and ignitioncoil 14 are applied to a control unit 15 which drives the injector 10 atan injection pulse width dependent on the signals, as describedhereinafter in detail.

Output signals of the air flow meter 3 and engine speed sensor 11 arefed to a basic injection pulse width calculator 16 which produces abasic injection pulse width signal T_(P). A correcting coefficientcalculator 17 is applied with the output signal of the coolanttemperature sensor 13 to generate a correcting coefficient signal K forthe open loop control. The output signal of the O₂ -sensor 12 passesthrough an O₂ -sensor warm-up detector 20 and air-fuel ratio detector 21to a correcting coefficient calculator 22 which produces a correctingcoefficient signal α for the closed loop control.

The basic injection pulse width signal T_(P) and correcting coefficientsignals K and α are applied to an injection pulse width calculator 23which produces an injection pulse width signal Ti. A driver 24 respondsto the signal Ti and produces a driving output which is fed to theinjector 10 to drive it.

On the other hand, the output signal of the ignition coil 14 is appliedto an engine start detector 18 which produces an engine start signalwhen the engine is started. The engine start signal causes a timer 19 tooperate to count down a stored number. The timer produces a timer signalfor a set time (for example 10 sec.). In response to the timer signal,the warm-up detector 20 produces a high level reference voltage (forexample 500 mV) for the set time after the engine start. The warm-updetector 20 compares the output voltage of the O₂ -sensor with the highlevel reference voltage. When the output voltage exceeds the referencevoltage, the warm-up detector produces a feedback control start signalwhich is fed to the air-fuel ratio detector 21, so that air-fuel ratiocontrol operation by the feedback signal from the O₂ -sensor starts.When the timer 19 counts the stored number (ten seconds), the timersignal disappears, so that the warm-up detector 20 produces a low levelreference voltage (400 mV) to compare the output voltage of the O₂-sensor with the low level reference voltage.

The operation of the system is described hereinafter with reference toFIG. 2. At a step S₁, it is determined whether the engine is started.Since the engine does not start immediately after closing an ignitionswitch, the program proceeds to a step S₂ at the first cycle of theprogram. At the step S₂, a predetermined number corresponding to the settime (10 sec.) is stored in the timer 19. In the next program, if theengine is started, the program proceeds to a step S₃ where it isdetermined whether the timer 19 is cleared (stored number is zero). Whenthe timer has a stored number, the number is continuously decremented byone at a step S₄. At a step S₅, if the stored number is not yet zero,the program goes to a step S₆, where the reference voltage is set to thehigh level (500 mV). If the timer is cleared at step S₃ or S₅, theprogram proceeds to a step S₇, where the low level reference voltage(400 mV) is set.

Thus, in the system of the present invention, the reference voltage fordetecting the activation of the O₂ -sensor is set to a high value for aset time after starting the engine. Accordingly, the detection of theactivation can be done without malfunction, and the feedback controloperation by the feedback signal of the O₂ -sensor is started at aproper time. Further, since the reference voltage is changed to a lowlevel when a set time elapses after starting the engine, the feedbackcontrol operation starts at a proper time at cold engine operationwithout delay.

While the presently preferred embodiment of the present invention hasbeen shown and described, it is to be understood that this disclosure isfor the purpose of illustration and that various changes andmodifications may be made without departing from the spirit and scope ofthe invention as set forth in the appended claims.

What is claimed is:
 1. In an air-fuel ratio control system for anautomotive engine, the system having an O₂ -sensor producing outputvoltage relative to oxygen concentration of exhaust gases of the engine,a feedback control system responsive to the output voltage of the O₂-sensor for controlling air-fuel ratio of mixture supplied to theengine, the improvement comprising:detecting means for detectingstarting of the engine and for producing an engine start signal; a timerresponsive to the engine start signal for producing a first timer signalduring a predetermined period of time and for producing a second timersignal after the predetermined period of time; O₂ -sensor warm-updetecting means responsive to the first timer signal for comparing theoutput voltage of the O₂ -sensor with a high level reference voltage andfor producing a feedback control start signal when the output voltage ofthe O₂ -sensor exceeds the high level reference voltage, and responsiveto the second timer signal for comparing the output voltage of the O₂-sensor with a low level reference voltage which is lower than the highlevel reference voltage and for producing the feedback control startsignal when the output voltage of the O₂ -sensor becomes higher than thelow level reference voltage; means responsive to the feedback controlstart signal for starting operation of the feedback control system. 2.The system according to claim 1 wherein the first-mentioned detectingmeans is responsive to a signal from an ignition coil of the engine forproducing the engine start signal.
 3. The system according to claim 1wherein the timer is a counter in which a desired number can be stored.4. The system according to claim 1, further comprisingmeans for storinga number representing the predetermined time when the first-mentioneddetecting means does not produce the engine start signal, and said timerfor decrementing the stored number to zero thereafter when thefirst-mentioned detecting means produces the engine start signal,whereupon said O₂ -sensor warm-up detecting means provides the low levelreference voltage, and wherein, during said decrementing before zero isreached said O₂ -sensor warm-up detecting means produces the high levelreference voltage.